Power line carrier system



July 21, 1936.

H. A. AFFEL Er AL POWER LINE CARRIER SYSTEM Filed Dec. l2, 1930 Pou/e1* Generator ATTORNEY 25 terminals of the carrier system.

Patented July Y121, 1936 PATENT OFFICE 2.048.091 I Powna LINE Cananea SYSTEM Herman A. Aflel, Ridgewood, and Estlll I. Green,

East Orange, N. J., assignors to American Telephone andmelegraphug Company, a corporation of NewY Application December 12, 1930, serial No. 501,984

' a claims. (ci. 117-352) This invention relatesto the transmission of signals at carrier frequencies over power lines,

and particularly tov means for terminating the.

power line for the said carrier frequencies-'to avoid reection effects, and means to effectively isolate a section of power line from its branches at carrier frequencies.

Since a power line network comprises numerous interconnections, loops, and spur lines, vit is less 1o well adapted for carrier communication than the ordinary telephone circuit- The reection effects resulting from the complex nature of the power line connections and also from the improper terminating impedances icausea carrierv cirl5 cuit, superimposed upon such a'power line, to

have characteristics that are extremely erratic in the range of frequencies employed. Furthermore, switching operations in the power system vwill have an important effect upon the carrier frequency characteristics.

For example, let it be assumed that a carrier system is superimposed upon a power transmission line that has a spur connection at a .point y along the main transmission line between the Unless such spur line is isolated from the main line in some way orV is terminated in an impedance approximating its characteristic impedance, the carrier frequency impedance that ispresented by the .30 spur line will vary widely with frequency and at certain frequencies will resemble a short circuit, thus preventing satisfactory transmission between the carrier terminals. 'Ihe 'employment oranti-resonant circuits or choke coils has been suggested as a remedy to prevent the disturbing effect produced by such detrimental paths. Such choke circuits have the disadvantage that their g impedance varies with frequency and that they may require tuning to the working frequency;

band of frequencies in the carrier' range, and requires no special tuning.

This invention furthermore resides in a network for reducing reflection effects'ln power lines,

by terminating the power lines at carrier i'rel quencies in their characteristic impedance.

Otherobjects of this invention will be apparent from the following description when readin connection with the attached drawing, of which Figure 1 shows schematically a transmission line adapted for the simultaneous transmission of power currents and carrier signaling currents embodying the series impedance network referred to hereinbefore; Figs. 2 and 3 show schematically other impedance networks that may be substituted for the impedance network shown in con- 5 nection with the spur line of Fig. l; Fig. 4 shows an arrangement of networks for terminating a power line; and Fig. 4a shows a terminating network fora three-phase line.

In Fig. 1 the line L represents the main transl0 mission line of a power system extending from a generator station A to aistation B at which there is a power load. Connected with the main line at C is a spur line that extends to another power load at station D. I and 2 represent carrier apl5 paratus that may be of any well-known type for the ,transmission of carrier frequency signals over the line L. The carrier apparatus' may be coupled to the po'wer line by means of coupling condensers 3 and 4 and 3' and I. Since carrier 20 apparatus is generally designed to match the inrpedance of the power line, a proper high-frequency termination is obtained wherever carrier apparatus is connected to the power line. As will later be shown, when a high-frequency termina- 25 `tion is desired at a point where carrierv apparatus sipation of the carrier-currents in that appara- 35 tus. Networks I0' and II', similar to I0 and II, are connected to the yconductors of line II at station B. By inserting networks, such as I0 and I I, in series with the line conductors, the said line, when looking in the direction of the genera- 4o I tor, is caused to have a high impedance at the carrier frequencies; and the use of properly designed carrier apparatus provides a smooth termination for the carrrier frequency currents employed. Similar networks at station B serve the 45 sam'e purpose as networks III and II, so that the transmission of carrier signals by. the apparatus I and 2 will be free from the diiliculties inherent Y in carrier signaling over power lines in which the improvements set forth hereinbefore are not employed.

The eiect upon carrier signaling of the lmpedance represented by the spur line connected with the main transmission line at C is prevented by the insertion of carrier-frequency impedance 55 networks in series with the conductors of the spur line. In the arrangement shown, it is assumed that the impedance networks can be placed at the junction of the spur line with the main line. To obtain a low impedance for the power frequencies it is necessary to use a shunt terminated lter whose shunt member includes an inductance connected directly across the two sides of the lter. Such construction makes it possible to connect in series 4with the line wire an inductance coil similar to a lightning arrester choke coil rand comprising one or two layers as desired.

In the drawing, the network I2 includes in a ir type filter section consisting of inductances Il" and I5 and condenser, I1, the inductance I3 being shunted by a resistance Il, and the inductance coil I5 being in series with the conductor of the spur line. Preferably the resistance I4 is made at least equal to the iterative impedance of the filter section. A spark gap I6 serves to protect the entire network. The network I2 uses a high f pass filter structure.

Fig. 4 shows a mode of treatment of the spur.

line when it is not desired to insert the series highimpedance networks in the spur line at the.. junction. with the main line. In such a case,

high-impedance networks III) and II, which may be similar to I2 of Fig. l, or to Fig. 2 or Fig. 3, are inserted in series with the spur line conductors near the point of connection of the power load D', thus rendering the power load a high im;- pedance at carrier frequencies; In some cases the networks Ill and II of Fig. 4 might consist of an inductance shunted by a condenser, or if the impedance of the power apparatus at carrier frequencies is high, they might be omitted entirely. To effect a smooth termination of the spur line throughout the range of carrier frequencies employed, a network 3 may be bridged across the spur line conductors. Thatnetwork comprises condensers l, 5, 6 and 1,- an inductance 8. and a resistance 9, which will be recognized as constituting a vfilter structure with terminating resistance. Preferably the resistance 9 is made substantially equal to Ithe iterative' impedance of the filter.. Thus network 3 terminates the line L in an impedance that is equal to'the characbe part of a multi-phase line. Fig. 4a shows a network for terminating a' three-phase line at high frequencies. In Fig. 4a the condensers 2l. 2|, 23, 2l, the inductance 26, and resistance 29 are connected across. the phase ab; condensers I9, 20, 22 vand 23. the inductance 25, and resistrier frequency range.

ance 28 are connected across the phase bc; and

the condensers I9, 2|, 22 and 2l, inductance 21, and resistance 30 are connected across the phase ac. Other well-known types of high-pass or band-pass filter structures may be used in Fig. 4 and Fig. 4a if desired.v

-r It is desirable to point out that the terminating networks shown in Figs. 4 and 4a may be advantageously employed in reducing the effect upon a power system of high frequency transient currents that result from short circuits, lightning, or other causes in or adjacent to such system. Such networks may be inserted in a power line at the terminals or other points where impedance -irregularities are present. Since those networks effectively terminate the line in an impedance simulating the characteristic impedance of the line throughout theshigher frequency range, they prevent the building up of high potentials by resonance action when the line is vshocked by transients, lightning, etc. No loss is introduced by the networks to thepower currents. While the invention has been disclosed as embodied in certain forms, it is to be understood that such showing is purely schematic and is not intended to limit the invention, as defined in the following claims.

What is claimed is:

1. Ina systen for the simultaneous transmisn sion of low frequency` currents and carrier frequency signaling currents, the combination with a power circuit having a load at the end thereof, of a network connected near the end of the said circuit for terminating'it in the carrier frequency range, the said network presenting at high frequencies a constant impedance substantiallyv equal to the characteristic impedance at those Y high frequencies of the power circuit to which it is connected and presenting at low frequencies a very high impedance, the said network being terminated in a resistance substantially equal to the iterative impedance of the network.

2. In combination, a three-phase power transsion of low frequency currents and carrier frequency signaling currents, the combination with a power circuit having a load at the end thereof. of a terminating network, connected near the end of the said circuit for terminating it inv the carrier frequency range, the said terminating network for carrier frequency currents being bridged across the circuit conveying the said currents and comprising condensers in series with an inductance bridged across the said circuit-anticondensers in series with a 'resistance connected in 'shunt with the said inductance, the said resist- 'ance being substantially equal to the iterative impedance of 'the said network throughout the car- HERMAN A. AFFEL. ES'IILI.v I. GREEN. 

